After A has finished 1/2 of a piece of work in 10 days; B joins him after 5 days. Later A completes the work in 4 more days. In how many days would B alone complete the work?
- 100 days
- 120 days
The Usual Method
If A finishes 1/2 of the work in 10 days, it would take 20 days for A to finish the work alone. Assume that B takes ‘2’ days to complete the work alone. Thus in 1 day, B will do of the work. So, in 5 days, B will finish of the work.
Work done by A in 5 days =
Work done by A in 4 days =
The work done by A & B in sequence as mentioned in the question is:
(by A) + (by A) + (by B) + (by A) = 1
Hence, + + + = 1
Estimated Time to arrive at the answer = 75 seconds.
Presently A works for a total of 10 + 5 + 4 days, i.e 19 days. A alone can finish the work in 20 days. This means that contribution of B is equivalent to saving 1 days work of A or of the total work. B contributes this of the work by working for 5 days, so in 1 day, B will do of the work. Thus, B will take 100 days to finish the work alone.
Estimated Time to arrive at the answer = 10 seconds.